Steam generators



Sept. 18, 1962 V J. A. FABREGAS STEAM GENERATORS s Sheets-Sheet 1 Filed Nov. 16, 1959 FIG.I

JOSEPH AFABREGAS IN V EN TOR.

ATTORNEY J. A. FABREGAS STEAM GENERATORS Sgpt. 18, 1962 3 Sheets-Sheet 2 Filed Nov. 16, 1959 FIG.2

"lrlrllllli FIG-3 JOSEPH A-FARGAS H6 INVENTOR.

BY kma. w

- fit ATTORNEY P 1962 J. A. FABREGAS 3,054,599

STEAM GENERATORS I Filed Nov. 16, 1959 3 Sheets-Sheet s JOSEPH AFABFEGAS IN VEN TOR.

ATTORNEY United States Patent 3,054,599 STEAM GENERATURS Joseph A. Fabregas, Schenectady, N.Y., assignor, by mesne assignments, to the United States of America as represented by the United States Atomic Energy Commission Filed Nov. 16, 1959, Ser. No. 853,098 3 Claims. (Cl. 257-231) This invention relates to steam generators and particularly to steam generators of the class which use bayonet or spur tubes.

The use of bayonet tubes in steam generators or the like is well known. In one type of construction a set of dead end tubes, supported by a first tube sheet, is telescoped into a second set of tubes supported by a second tube sheet, the tube sheets being spaced from one another to form a chamber therebetween. Each of the smaller or inner tubes of such a construction extend into a corresponding outer tube to terminate adjacent the dead end of the outer tube. The peripheral walls of the inner tubes are spaced from the inner walls of the outer tubes to form an annular passage. A fluid to be heated enters the set of inner tubes and flows inwardly therethrough. Upon leaving the inner tubes, the fluid reverses direction and passes outwardly through the annular passage in heat exchange relation with the shell side fluid which is in continuous contact with the peripheral surfaces of the outer tubes. Steam thus produced in the annular passageways flows into the chamber between the first and second tube sheets and thence through an outlet provided in the shell.

In the construction herein invented, however, the foregoing result is produced although only one tube sheet is required. A bayonet tube of novel design is provided so that one of the tube sheets can be dispensed with. Moreover, the construction is such that steam generated in the tubes may pass upward through a feedwater baflie thus providing an integral feedwater heater within the steam generator.

The principal object of this invention, therefore, is to provide a steam generator utilizing bayonet tubes of novel design arranged so that only one tube sheet is required.

. Another object is to provide a steam generator so constructed that a novel and efficient feedwater heater is provided as an integral part thereof.

A further object is to provide a steam generator having bayonet tubes which may be individually replaced or repaired without having to disassemble the unit.

A still further object is to provide a novel bayonet tube assembly for a heat exchanger in which a set of outer tubes is conventionally secured to a tube sheet, each of such tubes having, however, a riser element extending beyond the tube sheet, the risers in turn serving to support the inner tubes and providing inlet means for the feedwater to enter the inner tubes.

A further object is to provide a novel bayonet tube unit in which the outer element supports the inner element and also provides inlet means for fluid to pass into the inner element through the outer element.

In the drawings,

FIG. 1 is a foreshortened cross sectional view of a steam generator of the present invention;

FIG. 2 is a partial cross sectional view on an enlarged scale of one of the bayonet tubes of the present invention as shown in FIG. 1;

FIG. 3 is a partial cross sectional view on an enlarged scale of an alternate construction of the riser of the bayonet tube assembly;

FIG. 4 is a cross sectional view of the bayonet tube assembly taken on line 44 of FIG. 3;

FIG. 5 is a partial plan view of the concentric locating rings for the bayonet tubes; and,

FIG. 6 is a partial plan view showing the feedwater tray.

Referring now to FIGS. 1 and 2, there is illustrated a steam generator comprising a cylindrical shell 10 having a spherical header 11 provided with a feedwater inlet 12 and a steam outlet 13. A tube sheet 14, secured to the shell 10 adjacent the upper end thereof, supports a plurality of dead end tubes 15 which are preferably welded thereto. An inner tube 16 (see FIG. 2) is disposed within each of the outer tubes 15, the upper end of each of the inner tubes 16 having a curved portion or elbow 13 the mouth of which registers with an opening 19 in the riser or outer tube extension 17. The open end or mouth of the elbow 18 is welded to the riser 17 adjacent opening 19 to provide for the flow of fluid into the tube 16. To assemble the inner tubes 16 into operative position in the outer tubes 15, the risers 17 are inserted within the tubes 15 in a tight forced fit so as to hold the inner tubes in position. Concentric rings 20 (see FIG. 5) held in position by spaced radially arranged supports 21 engage grooves 22 formed in the top of each of the risers 17 to hold the risers and inner tubes in desired service position. The inner tube 16 may also be provided with flexible sections 23 at spaced intervals along its length to facilitate the inserting of the inner tubes through an opening 24 in the shell. Tubes 15 are further provided with locating lugs 25 to maintain the inner tube 16 in spaced relation.

Arranged across the upper portion of the shell is a feedwater tray 26 (FIG. 6) to receive feedwater supplied through inlet 12. Supported by tray 26 and extending through a central opening therein is a cylindrical feedwater downcomer 27 which extends upwardly a selected distance above the tray and downwardly to a level selectively spaced above tube sheet 14. The distance downcomer 27 extends above tray 26 determines the water level maintained on the tray. Tray 26 is further provided with a great number of small apertures 28 through which steam passes upwardly into the water on the tray 26 and therethrough as hereinafter more fully described. Spaced a predetermined distance above the tray 26 is a feedwater inlet baffle ring 29 secured by conventional means to the channel 11 to provide for a uniform flow of feedwater from inlet 12 across the tray 26. The shell side fluid is conventionally supplied to the unit through fin inlet 30 and is discharged from the shell through out- In operation, feedwater delivered through inlet 12 flows on to tray 26 as controlled by baflle ring 29 and forms a pool 32, the level of which is determined by the extent that downcomer 27 projects above the tray. The water overflows the downcomer and passes downwardly therethrough to form a second pool 33 at the bottom of the header on the tube sheet 14. The water then passes from the lower pool through the openings in the side walls of the risers 17 into the inner tubes 16. Then the water flows downward through each of the inner tubes 16 to the open end thereof and reverses its flow to move upward through the annular passage 34 between the inner and outer tubes. Excellent heat exchange takes place since the outer tubes are in complete peripheral contact with the hot shell side fluid. The water in the annular passage ways is converted into steam which passes out the upper ends of the outer tubes through apertures 28 in the feedwater tray 26 and bubbles through the pool 32 upwardly into chamber 35 above the tray. Thence it is delivered through steam outlet 13 to a point of use. The steam passing through the feedwater in the pool 32 heats it to a predetermined amount, the arrangement thus functioning as an integral feedwater heater.

The level of pool 33 is maintained by conventional control devices which increases or decreases feedwater pump flow as required to maintain level within prescribed Patented Sept. 18, 1962 3 limits. A device of the type shown in US. Patent 2,756,028 may be used.

Although the level of pool 33 is shown and described as maintained below the top of risers 17, it should be understood that the risers may be completely submerged in the pool. In such an arrangement, water will be prevented from flowing into the top of the risers 17 by the upflowing high velocity stream of steam-water mixture. It should here be observed that during operation the water collected on tray 26 is prevented from dripping through openings 28 by the pressure of the steam: thereunder.

Referring now to FIG. 3, there is shown an alternate construction for locating the inner tube 16 within the outer tube 15. In this embodiment, tube sheet 14 is provided with a trepanned boss 14a to which the tube 15 is securely welded. The inner tube 16 is arranged within the riser and secured thereto in the same manner described for the first construction. The riser 17 is enlarged at its lower end to provide a flange 17a dimensioned to fit tight- 1y over boss 14a to securely locate the inner tubes 16 within the outer tubes 15.

While there has been hereinbefore described an approved embodiment of this invention, it will be understood that many and various changes, arrangement of parts and details of construction thereof may be made without departing from the spirit of this invention, and that all such changes that fall within the scope of the ap-' pended claims are contemplated as a part of this invention.

What I claim is:

l. A steam generator comprising a shell; a header hav-' ing feedwater inlet means and steam outlet means; a tube sheet defining a chamber within the header; a set of outer tubes supported at one end by the tube sheet and extending therefrom into the interior of the shell, the end of each of such tubes within the shell being closed and the end of each of such tubes at the tube sheet being open and in communication with the chamber within the header; an open ended riser tube in communication with each of said outer tubes and extending into the header chamber, each of said riser tubes having an opening through its side wall; a set of inner bayonet tubes each one of which is telescoped into one of the outer tubes to form an annular passageway therebetween, one end of each inner tube being open and disposed adjacent the closed end of an outer tube and the other end of each tube being open and in communication with the opening in the sidewall of the associated riser; a tray in the header to collect feedwater in a pool, said tray having a multiplicity of small apertures and a large central opening through its bottom; and a downcomer supported by the tray to conduct feedwater from the tray to the bottom of the header to form a lower pool to supply the aforesaid inner tubes through the riser openings, the arrangement of the parts being such that feedwater from the lower pool passes into the bayonet inner tubes where it is converted into steam to pass 4 through the annular passageways into and through the risers thence to pass through the apertures in the tray to bubble through the feedwater on the tray and thence pass out of the steam generator through the steam outlet means in the header.

2. A steam generator comprising a shell; a header having feedwater inlet means and steam outlet means; a tube sheet defining a chamber within the header; a set of bayonet tube assemblies, eachassembly including inner and outer tubes extending into the interior of the shell, each outer tube element being supported by the tube sheet; a riser tube in communication with the outer tube of each bayonet assembly and extending upwardly from the tube sheetv into the header chamber, each riser having an opening in its side wall for connection with the inner tube of the associated bayonet assembly; means securing each inner tube to the riser associated with its assembly at said side wall opening to establish communication between the inner tube and the exterior of the riser; a tray in the header to collect feedwater in a pool, said tray having a multiplicity of small apertures and a large central opening through its bottom; and a downcomer supported by the tray to conduct feedwater from the tray to the bottom of the header to form a lower pool to supply the aforesaid inner tubes through the riser openings, the arrangement of the parts being such that teedwater from the lower pool passes into the bayonet inner tubes where it is converted into steam while passing through the annular passageway and through the risers thence to pass through the apertures in the tray to bubble through the feedwater tray and to pass out of the steam generator through the steam outlet means in the header.

3. A steam generator comprising a shell; a header having a chamber therein; means to supply feedwater to the header; a steam outlet in the header; a tube sheet; a set of bayonet tube assemblies including inner and outer tubes, the outer tubes being supported by the tube sheet and extending into the shell; a riser tube extending into the header chamber to establish communication between each of said outer tubes and said chamber, each riser tube having an opening in its side wall; a curved upper end portion on each inner tube terminating in registration with the side wall opening of the riser to establish communication between the header chamber and the inner tube, the opposite end of the inner tube terminating adjacent the end of the associated outer tube; means securing said curved end portion to the riser; an inlet to supply feedwater to said header chamber whence it passes through the inner tubes to the outer tubes where it is converted to steam; an inlet in the shell to supply shell side heating fluid to flow across the bayonet tube assemblies; and an outlet for such fluid.

References Cited in the file of this patent UNITED STATES PATENTS 1,919,335 Kerr et al. July 25, 1933 

